If you store passwords you should use a program like
lastpass which encrypts everything. It's always good to have an antivirus with email protection, and malware protection.
AVG free is more than adequate for this purpose.
Another thing to consider is no one may have 'hacked' your account. The hacking term is used to loosely these days. 98% of the time if someone has had their logins compromised it's their own fault. Someone may simply just be 'spoofing' your email to use in their spam emails. This is very common. To put it simply it just means they are altering the email headers to make it appear that you are sending the email. It happens quite often and there is pretty much nothing you can do about it.
Unfortunately I just cleared my spam folder out and have no examples I can show you of an email header that's been spoofed. You might be able to find one on google though and have the person saying they getting mail from you forward the spam to you then you can take a look at the headers and see if you beings spoofed.